3. A burette. A graduated tube which, when filled to O, holds 100 cubic centimètres, and is divided into 100 equal parts.
(One cubic centimètre is the volume of one gramme of distilled water at 4° C.[230], 1000 cubic centimètres equal 1 litre).
[230] It is customary to make the measurements with metrical apparatus at 60° Fahr.
Volumetric solutions, before being used, should be shaken in order that they may be throughout of uniform strength. They should also be preserved in stoppered bottles. All measurements should be made at 60°.
Volumetric Solution of Bichromate of Potash (Bichromate of potash, KO,2CrO3 = 147·5, or K2Cr2O7 = 295).
| Take of— | |
| Bichromate of potash | 147·5 grains. |
| Distilled water | a sufficiency. |
Put the bichromate of potash into the 10,000 grain flask, and, having half filled the flask with water, allow the salt to dissolve; then dilute the solution with more water, until it has the exact bulk of 10,000 grain-measures: 1000 grain-measures of this solution contain 14·75 grains of the bichromate (1⁄10th of K2CrO3, or 1⁄20th of K2Cr2O7 in grains), and, when added to a solution of a protosalt of iron, acidulated with hydrochloric acid, are capable of converting 16·8 grains (1⁄10th of 6Fe, or 1⁄20th of 6Fe in grains) from the state of protosalt to that of persalt grammes, and cubic centimètres may be employed instead of grains and grain-measures; but for convenience 1⁄10th of the numbers should be taken. Thus, 14·75 grammes of bichromate of potash should be made to form 1000 cubic centimètres of solution. 100 cubic centimètres of this solution contain 1·475 grammes of the bichromate (1⁄100th of KO,2CrO3, or 1⁄200th of K2Cr207 in grammes), and, when added to a solution of protosalt of iron acidulated with hydrochloric acid, are capable of converting 1·68 grammes of iron (1⁄100th of
6Fe, or 1⁄200 of 6Fe, in grammes) from the state of protosalt to that of persalt.
This solution is used for determining the proportion of protoxide of iron in the following preparations. It is known that the whole of the protosalt has been converted into a persalt when a minute drop of the liquid, placed in contact with a solution of red prussiate of potash on a white plate, ceases to strike with it a blue colour.
| British Weights and Measures. | Metrical Weights and Measures. | |||||||
| Grains weight of substance. | = | Grain measures of vol. sol. | Grams weight of substance. | = | C. C. of vol. sol. | |||
| Ferri | arsenias | 20 | = | 170 | or | 2·0 | = | 17·0 |
| ” | carb. sacch. | 20 | = | 330 | ” | 2·0 | = | 33·0 |
| ” | oxid. magn. | 20 | = | 83 | ” | 2·0 | = | 8·3 |
| ” | Phosphas | 20 | = | 250 | ” | 2·0 | = | 25·0 |